1. Field of the Invention
This invention relates to a light emitting device, more particularly to a white light emitting device having two wavelength-converting layers.
2. Description of the Related Art
FIG. 1 illustrates a conventional white light emitting device that includes a die-mounting cup 11, a blue light emitting diode 12 mounted in the die-mounting cup 11, and a phosphor layer 13 enclosing the blue light emitting diode 12 for converting blue light into yellow light. Mixing of blue light and yellow light produces white light. However, due to a higher light intensity and a shorter traveling length at a normal direction (Ln) of the blue light emitting diode 12 than at side directions (Ls), the white light emerging from the side directions (Ls) is likely to be yellowish and the light emerging from the normal direction (Ln) is likely to be bluish. FIG. 2 shows the measured x and y coordinate chromatic values of the conventional white light emitting device measured according to the color model of the Commission International del'Eclairage (CIE). The results show that the chromatic value of the aforesaid conventional light emitting device for each x and y coordinate is a curve throughout different angles and has a lowest value at the normal direction (Ln), i.e., at zero degree angle, and a highest value at each of the side directions (Ls), i.e., at angles above 60 degrees. This color deviation is undesired and is gradually enlarged with the increase of the angle relative to the normal direction, which results in non-uniform light. In addition, the color deviation will be worsened in current LED development and new applications, which use a high power light emitting diode and a large die-mounting cup.